i) Field of the Invention
This invention relates to a method of producing a value product from a source of lime, which may be an industrial inorganic byproduct such as cement kiln dust and a coal ash of high carbon content which is an industrial inorganic byproduct.
The method exploits heat generated from combustion of the carbon content of the coal ash and hot combustion gases evolved also provide a source of heat energy which can be recovered.
ii) Description of Prior Art
Coal ashes, namely bottom ash and fly ash are produced as byproducts in the burning of coal and are collected in industrial installations in a particulate form for disposal. Fly ash is produced in a fine particle form.
Coal ashes are pozzolanic and are employed as supplementary materials in cements, however, a significant carbon content in coal ashes limits their use in cements in the absence of steps to remove the carbon from the coal ash.
In the case of coal ashes having a carbon content above about 3%, by weight, methods have been developed which can remove the carbon so that the coal ash can be employed as a cement supplement. The methods include separation systems which produce a waste stream of mixed ash and carbon as well as a low carbon ash stream; and combustion of the carbon producing an ash stream and heat which may not be usable. These methods are not as practicable or economical for high carbon coal ashes having a carbon content above about 10%, by weight.
Thus, coal ashes of high carbon content can not be employed as supplementary cement material, and represent a disposal problem.
Cement kiln dust is a byproduct of cement processing and is produced in fine particulate form and is composed of partly and fully calcined calcium carbonate, thus it comprises calcium carbonate and calcium oxide (lime).
Cement plants may produce cement kiln dust (CKD) in differing quantities, even as high as 200,000 tons of cement kiln dust annually, and the CKD represents a disposal problem.
Cement kiln dust has been employed in cement production, but its fineness represents a handling problem and its use limited by chemistry.
Blast furnace slag is a significant supplementary cement material, however, manufacture of such cement material is limited to slag supplied by iron blast furnaces having slag quenching facilities.
It is an object of this invention to produce a synthetic slag comparable to blast furnace slag and which can be employed as a supplementary cement material, or lightweight aggregate.
It is a further object of this invention to produce such a synthetic slag employing a source of lime, which may be, for example, cement kiln dust; and coal ash of high carbon content.
It is still a further object of this invention to provide a method for producing such a synthetic slag, which exploits heat of combustion of the high carbon content of coal ash.
It is yet a further object of this invention to provide such a method with removal of hot combustion gases and recovery of the heat energy of such gases.
In accordance with the invention there is provided a method of producing a value product from a source of lime and coal ash comprising: a) establishing an initial melt of an inorganic material providing a source of lime and a coal ash having a high carbon content, b) adding fresh amounts of said inorganic material and said coal ash to said initial melt, c) oxidising the carbon content of said coal ash in said melt with generation of heat, and exploiting the generated heat in the melting of said fresh amounts to produce an enlarged melt of molten calcium aluminosilicate material, and d) recovering a value product from said enlarged melt.